Abstract : The recent development of genetically encoded
calcium indicators enables monitoring in vivo the
activity of neuronal populations. Most analysis of
these calcium transients relies on linear regression
analysis based on the sensory stimulus applied or the
behavior observed. To estimate the basic properties of
the functional neural circuitry, we propose a networkbased
approach based on calcium imaging recorded at
single cell resolution. Differently from previous
analysis based on cross-correlation, we used Grangercausality
estimates to infer activity propagation
between the activities of different neurons. The
resulting functional networks were then modeled as
directed graphs and characterized in terms of
connectivity and node centralities. We applied our
approach to calcium transients recorded at low
frequency (4 Hz) in ventral neurons of the zebrafish
spinal cord at the embryonic stage when spontaneous
coiling of the tail occurs. Our analysis on population
calcium imaging data revealed a strong ipsilateral
connectivity and a characteristic hierarchical
organization of the network hubs that supported
established propagation of activity from rostral to
caudal spinal cord. Our method could be used for
detecting functional defects in neuronal circuitry
during development and pathological conditions.